Theory 35/Aerospace Structures
Fatigue Follows Spectrum Severity
The claim
Fatigue life under variable amplitude loading is set by the ratio of spectrum severity to the design spectrum rather than by the number of cycles.
01Mechanism
Damage accumulates with stress range to a power; a mild spectrum flown often can do less damage than a severe one flown rarely.
02Predictions
- P1Life should track the severity ratio.
- P2Cycle count alone should mispredict.
03Refutation
Life tracking cycle count would remove the severity.